1. Field of the Invention
The present invention relates to a pump wherein a piston is slid within a cylinder to produce positive and negative pressure to suck and discharge ink from, for example, nozzles of an ink jet print head in an ink jet printer.
2. Description of the Related Art
Suction pumps have been used to clean nozzles of an ink jet type printer to prevent clogging of the nozzles or to unclog clogged nozzles. The suction pump includes a cylinder and a piston slidably disposed within the cylinder. The cylinder and the piston form therebetween a pump chamber with variable volume depending on the sliding position of the piston.
Japanese Patent Application (KOKAI) No. HEI-8-174853 describes the conventional suction pump shown in FIG. 1. The suction pump includes a cylinder 208, two pistons 200, 201, forming a pump chamber in the cylinder, drive shafts 202, 203, which are linked with the pistons 200, 201 respectively, and a suction tube 209 fluidly connected with the interior of the cylinder. A cam 204 driven to rotate in a direction indicated by an arrow A is provided with cam grooves 206, 207. Tips of the drive shafts 202, 203 are connected with the cam grooves 206, 207 respectively so as to be guided thereby. By changing the interval and position of the two pistons 200, 201 in the cylinder 208, a negative pressure develops in the suction tube 209. Although not shown in the drawings, the suction tube 209 is connected to a suction cap which can be brought into intimate sealed contact with ink jet nozzles formed in a print head of an ink jet type printer. When the negative pressure develops in the suction tube 209, ink and undesirable material mixed therein is sucked from the ejection nozzles and discharged to a liquid waste foam (not shown in the drawings).
The drive shafts 202, 203 are connected to respective cam grooves 206, 207 by pins 210, 211 provided to the respective drive shafts 202, 203. In association with rotation of the cam 204, the pins 210, 211 follow the side surfaces 206a, 206b, 207a, and 207b of the cam grooves 206, 207 so that the pistons 200, 201 move reciprocally within the cylinder 208.
However, during pumping operations, not only do the drive shafts 202, 203 move reciprocally in an axial direction of the drive shafts 202, 203 indicated by an arrow B, but rotation of the cam 204 also applies to the tips of the drive shafts 202, 203 a large vertical force in a right angle direction, that is, a direction indicated by an arrow C, which is perpendicular to the axial direction of the drive shafts 202, 203. Because the drive shafts 202, 203 protrude from the cylinder 208 toward the cam 204, the force applied to the pins 210, 211 of the drive shafts 202, 203 in the direction indicated by the arrow C swings or vibrates the tips of the drive shafts 202, 203 so that the shafts can become shifted out of proper alignment.
As shown in FIG. 1, the cam 204 is supported on a support member 212. A swing stop plate 214 for preventing the drive shafts 202, 203 from swinging in the direction indicated by the arrow C is formed from a portion of the support member 212. A great deal of vibration is prevented by the swing stop plate 214.